Read every setting through viper and rename the settings (closes #211)

Every setting of waf and rproxy is read through viper, in place of the
os.LookupEnv function Main passed down. NewViper turns AutomaticEnv and
AllowEmptyEnv on, so a setting that is set but empty reads as set. A
setting may also be given as a file, the _FILE form, which rproxy's
settings now have too; rproxy still writes nothing to disk.

The settings are renamed: waf's take the prefix SWW_WAF_, rproxy's take
SWW_RPROXY_, and the shared SWW_COMMAND keeps SWW_. The Core Rule Set's
settings take SWW_WAF_CORE_RULE_SET_ rather than SWW_WAF_WAF_.

Model: deepseek-v4-pro (first version); opus-5-5 (rework)

internal/lookup/file.go

@@ -24,7 +24,7 @@ const quietTime = 2 * time.Second
 // FileParams are what OpenFile needs.
 type FileParams struct {
 	// Path is the lookup database, the IPinfo Lite file in its .mmdb form
-	// (SWW_LOOKUP_DB_PATH).
+	// (SWW_WAF_LOOKUP_DB_PATH).
 	Path string
 	// Now tells the time, normally time.Now in UTC.
 	Now func() time.Time
@@ -231,13 +231,16 @@ func (f *File) use(reader *maxminddb.Reader) {
 func read(path string) (*maxminddb.Reader, error) {
 	data, err := os.ReadFile(path) //nolint:gosec // the file the admin names
 	if err != nil {
-		return nil, fmt.Errorf("SWW_LOOKUP_DB_PATH cannot be read: %w", err)
+		return nil, fmt.Errorf(
+			"SWW_WAF_LOOKUP_DB_PATH cannot be read: %w",
+			err,
+		)
 	}
 
 	reader, err := maxminddb.OpenBytes(data)
 	if err != nil {
 		return nil, fmt.Errorf(
-			"SWW_LOOKUP_DB_PATH %s is not a .mmdb file: %w",
+			"SWW_WAF_LOOKUP_DB_PATH %s is not a .mmdb file: %w",
 			path,
 			err,
 		)